Abstract
The formation of rooting zone in soil was investigated by a simple rhizotron-like apparatus, in which acrylic plates were used as translucent walls. The primary roots emerge acropetally from the stem which consists of successive "shoot unit"s. And the primary roots emerging early in the development from the lower "shoot unit"s tended to elongate horizontally, while those emerging from the upper "shoot unit"s tended to elongate obliquely and much later vertically. Therefore, the rooting zone in soil was formed as follows. The rooting zone primarily occupied horizontal part of thc soil. And continuously, accompanying the growth of the plant, the rooting zone spreaded obliquely from the base of the plant, and much later vertically. The mean elongation rate of the primary roots was estimated as 33 mm per day, and the maximum value was 110 mm per day. Though the mean elongation rate showed little difference among most primary roots examined, the elongation rate of those emerging later and elongating vertically was small.
